The Year in Science: Animals 1997

Man's Oldest Friend

When did the first wolf trade its wild ways and freedom for the occasional pat on the head and meal-ticket lifestyle of doghood? Fossils found in Germany some years ago suggested that the evolutionary path to pugs and other unlikely wolf heirs began around 14,000 years ago. But last June a researcher studying canine dna announced that wolves were domesticated much earlier, probably more than 100,000 years ago.

Evolutionary biologist Robert Wayne of ucla examined a stretch of mitochondrial dna from 140 dogs of 67 breeds and compared it with the same stretch from wolves, coyotes, and jackals. As one would expect, he found that dogs and wolves were genetically the most similar. Wayne also found a wide variety of dna sequences in dogs. The genetic base that established the first dogs seems to have been very broad, he says. A large population of wild wolves were responsible for the genetic diversity we see in dogs today.

Based on their mitochondrial dna, Wayne divided modern dogs into four separate groups, or clades. The clades reflect events deep in the canine past, and so have little to do with the familiar breeds, which were created by humans in the last few centuries. It is possible, he says, that the four clades mean that wolves were domesticated on four separate occasions. But he thinks it more likely that they were domesticated just once and that the clades arose later, when dogs interbred with wolves that were still wild. The dna sequences in one clade, for instance, from breeds as varied as basset hounds and German shepherds, were nearly identical to sequences in gray wolves from Romania and western Russia—suggesting a comparatively recent mix between those dogs and wolves.

But Wayne’s most surprising result is his calculation—based on the amount of time it takes for mitochondrial dna to accumulate mutations—of when that first domestication took place: 135,000 years ago. Even if it is only roughly accurate, the date is astonishing because domesticating wolves implies much more than merely capturing a few pups and taming them. They have to become stably integrated into a human society, says Wayne. They have to want to stay in that society more than they want to run away and join their wild brethren. That involves a socialization process that is quite profound. If you’re a nomadic hunting-gathering society, how do you stably get progeny of that first tame wolf to become members of your society? If you think about horses and cattle, what happens if you don’t confine them—they’re outta there.

Were humans capable of such a feat some 100,000 years before settling down to invent agriculture? At a time, incidentally, when Neanderthals were just entering their heyday? Wolves and humans were living in the same environments for perhaps half a million years, so there was ample time for interaction, says Wayne. And it’s interesting that a lot did happen around 100,000 years ago. Humans evolved bigger brains, they moved out of Africa—perhaps that’s when wolves were first domesticated.

Many researchers, however, feel that dating based on a molecular clock is suggestive at best; mitochondrial dna mutates rapidly, which makes it a better timepiece than ordinary dna from the cell nucleus, but it may not necessarily mutate at a constant rate. And archeologists have found no evidence of any sort of domesticated animal even remotely close to 135,000 years ago. That date has no possibility of being correct, says Stanford archeologist Richard Klein. The fossil record is the ultimate proof. But Wayne argues that the earliest dogs looked much like wolves and so may have been overlooked in the archeological record. He thinks they may have served as hunting companions.